1. Field of the Invention
The present invention is related to an over heat protection circuit for a brushless dc motor. More particularly, the present invention is related to an over heat protection circuit having a thermal sensitive resistor to detect an operational temperature of a motor, thereby cutting off a motor current passing through a coil, when overheated, to protect the motor.
2. Description of the Related Art
A conventional over heat protection circuit is consisted of a complicated circuit and comprised of a thermal sensitive resistor incorporated into the complicated circuit. The thermal sensitive resistor of the over heat protection circuit has a changeable characteristic of resistance that is in response to changing of an operational temperature of a brushless dc motor. To accomplish protection of the motor, the over heat protection circuit must cut off a motor current when overheated, or change a rotational speed of the motor according to the operational temperature. However, the over heat protection circuit includes too many electronic components, such as resistors, a programmable chip, a pulse width modulator, transistors, capacitors, and diodes etc, and it may increase manufacture cost. Moreover, various drive circuits of the brushless dc motor requires different thermal resistance to constitute various driving modules that results in an incompatible problem. Consequently, a single over heat protection circuit cannot be empolyed in various drive circuits of the brushless dc motor.
The present invention intends to provide an over heat protection circuit for a brushless dc motor, which is consisted of a thermal sensitive resistor, a resistor and a transistor to form a simplified circuit for cutting off a motor current, when overheated, that may avoid destruction of the motor. Thereby, the over heat protection circuit accomplishes a simplified circuit, low manufacture cost and various design choice in such a way to mitigate and overcome the above problem.